Coating of hydraulic fracturing (or fracking) sand is not new. Millions of tons of sand or proppant are used in the oil and gas industry every year to stimulate wells and thereby improve productivity. Such sand may be coated to impart specialized functionality when in use in the down-hole environment. The sand “props open” the fractures in the well so that fluids and gas can escape more efficiently. The typical sand coating is either heat or chemically activated so that the sand will “stick” to itself forming a discrete “pack” or sponge like formation with open pathways for the fluid and gas to escape. Once the well is depleted, the sand pack can be “broken” or dissolved so the sand can flow back out of the well and be recovered. Uncoated sand is however, the largest percentage of fracking sand used in the industry.
Uncoated sand can fracture during handling operations creating very fine particles or dust. This dust is primarily composed of crystalline silica which is a known carcinogen. The handling of sand from mining, transport and handling can create large amounts of dust containing crystalline silica, which can be toxic at low inhalation levels. Reducing the risk to persons involved in handling hydraulic fracturing sand is a responsible and sustainable goal.
A number of references in the art are directed to coating hydraulic fracturing sand with a variety of materials, such as the use of thermoplastic coatings.
U.S. Pat. No. 6,582,819, issued to McDaniel et al., provides low density composite particles made of a binder and filler material for use in subterranean formations. The filler includes low density filler and optionally other filler. The binder includes a polymer and optionally cement. The binder is said to be at least one member of the group consisting of epoxy resin, polyurethane resin, alkaline modified phenolic resole curable with ester, melamine resin, urea-aldehyde resin, urea-phenol-aldehyde resin, furans, synthetic rubber, polyester resin, and further comprises cross-linking agents and conventional additives. The particles are said to be useful as proppants to prop open subterranean formation fractures. The particles are also said to be useful for gravel packing in subterranean formations, water filtration and artificial turf for sports fields. Methods of making the composite particles are also disclosed.
McDaniel et al., in U.S. Pat. No. 6,632,527, disclose composite particles made of a binder and filler material for use in subterranean formations. The filler is finely divided mineral and optional fiber. The binder is said to be at least one member of the group consisting of inorganic binder, epoxy resin, novolak resin, resole resin, polyurethane resin, alkaline phenolic resole curable with ester, melamine resin, urea-aldehyde resin, urea-phenol-aldehyde resin, furans, synthetic rubber, polyester resin, and further comprises cross-linking agents and conventional additives. The particles are proppants said to be useful to prop open subterranean formation fractures. The particles are also useful for water filtration and artificial turf for sports fields. Methods of making the composite particles are also disclosed.
U.S. Pat. No. 7,153,575, issued to Anderson et al., teaches coated particulate matter wherein the particles are individually coated with a first set of one or more layers of a curable resin, for example, a combination of phenolic/furan resin or furan resin or phenolic-furan-formaldehyde terpolymer, on a proppant such as sand, and the first set of layers is coated with a second set of one or more layers of a curable resin, for example, a novolak resin with curative. Methods for making and using this coated product as a proppant, gravel pack and for sand control are also disclosed.
McCrary et al., in U.S. Pat. No. 7,624,802, teach free flowing coated particles and low temperature methods of making the same. Each particle has a curable coating disposed upon a substrate. The substrate is a particulate substrate including an inorganic material, a particulate substrate including an organic material, a composite substantially homogeneous formed particle including a first portion of an at least partly cured binder and filler particles, or a hybrid particle having an inorganic particle as a core and a composite coating including at least partially cured resin and filler. The curable coating includes a continuous phase including resole resin and reactive powder particles embedded or adhered to the continuous phase. The reactive powder particles typically include resole resin, novolak resin, polyester, acrylic and/or urethane. A method including applying a coating including the continuous phase including resole resin and reactive or non-reactive powder particles embedded or adhered to the continuous phase.
U.S. Pat. No. 8,133,587, issued to Rediger et al., discloses thermoplastic coated proppants and methods for preparing the thermoplastic coated proppants. Methods for using these proppants in subterranean well formations and hydraulic fracturing operations, for example, are also disclosed. The thermoplastics are selected from a polyethylene, a polypropylene, an ethylene vinyl acetate, an ethylene ethyl acrylate, a styrene-isoprene-styrene, an acrylonitrile-butadiene-styrene, a styrene-butadiene-styrene, a polystyrene, a polyurethane, an acrylic polymer, a polyvinyl chloride, a fluoroplastic, a pine rosin (e.g., tall oil rosin, wood rosin, and gum rosin), a modified rosin (e.g., disproportionated rosins, hydrogenated rosins, polymerized or oligomerized rosins, Diels-Alder rosin adducts), a rosin ester (e.g., hydrogenated rosin esters, polymerized rosin esters, phenolic-modified rosin esters, dibasic acid-modified rosin esters; the rosin esters can be derived from tall oil rosin, wood rosin, and/or gum rosin), a polysulfide, a styrene-acrylonitrile, a nylon, a phenol-formaldehyde novolak resin, or a combination thereof.
U.S. Pat. No. 8,763,700, issued to McDaniel et al., discloses proppants for use in fractured or gravel packed/frac packed oil and gas wells with a contaminant removal component to remove one or more of the contaminants found in subterranean water/hydrocarbon from a production well. The water/hydrocarbon cleaning proppant solids may be used as discrete particles in a proppant formulation, as a coating on proppant solids in pores of a porous proppant solid or as part of the proppant's internal structure. The contaminant removal component removes contaminants, especially dissolved contaminants, in the subterranean water or hydrocarbon before the water/hydrocarbon leaves the well. For those contaminant removal components that can be regenerated, such as ion exchange resins, a measured quantity of an acidic regeneration solution can be injected into the fractured stratum for regeneration and recovered when the well resumes production.
U.S. Published Patent Application No. 2013/0065800, in the of McDaniel et al., discloses solid proppants coated with a coating that exhibits the handling characteristics of a pre-cured coating while also exhibiting the ability to form particle-to-particle bonds at the elevated temperatures and pressures within a wellbore. The coating includes a substantially homogeneous mixture of (i) at least one isocyanate component having at least 2 isocyanate groups, and (ii) a curing agent comprising a monofunctional alcohol, amine or amide. The coating process can be performed with short cycle times, e.g., less than about 4 min., and still produce a dry, free-flowing, coated proppant that exhibits low dust characteristics during pneumatic handling but also proppant consolidation down-hole for reduced washout and good conductivity. Such proppants are said to form good unconfined compressive strength without use of an bond activator, are substantially unaffected in bond formation characteristics under down-hole conditions despite prior heat exposure, and are said to be resistant to leaching with hot water.
McCrary et al., in U.S. Published Patent Application No. 2013/0186624, discuss solid proppants coated in a process that includes the steps of: (a) coating free-flowing proppant solids with a first component of either a polyol or an isocyanate in mixer; (b) adding a second component of either an isocyanate or a polyol that is different from the first component at a controlled rate or volume sufficient to form a polyurethane coating on the proppant solids; and (c) adding water at a rate and volume sufficient to retain the free-flowing characteristics of the proppant solids.
U.S. Published Patent Application No. 2014/0274819, in the name of McCrary et al., discloses proppants for hydraulic fracturing of oil and gas wells coated with a polyurea-type coating. In a preferred embodiment, the polyurea-type coating is formed by contacting a polymeric isocyanate with an amount of water and a blowing catalyst at a rate and quantity sufficient to generate a reactive amine in situ on the outer surface of the proppant which thereby reacts with unconverted polymeric isocyanate to form a thin polyurea-type surface coating that is substantially solid and lacks foam or substantial porosity. Alternatively, the polyurea-type can be produced by selecting reactive amine compounds and isocyanates to develop the coated proppant. The coated proppants retain the discrete, free-flowing character of the original core solids but with the beneficial effects of the polyurea-type coating of the present invention.
McDaniel et al., in U.S. Published Patent Application No. 2014/0309149, provide proppants for use in fractured or gravel packed/frac packed oil and gas wells with a contaminant removal component to remove one or more of the contaminants found in subterranean water/hydrocarbon from a production well. The water/hydrocarbon cleaning proppant solids may be used as discrete particles in a proppant formulation, as a coating on proppant solids in pores of a porous proppant solid or as part of the proppant's internal structure. The contaminant removal component removes contaminants, especially dissolved contaminants, in the subterranean water or hydrocarbon before the water/hydrocarbon leaves the well. For those contaminant removal components that can be regenerated, such as ion exchange resins, a measured quantity of an acidic regeneration solution can be injected into the fractured stratum for regeneration and recovered when the well resumes production.
U.S. Published Patent Application No. 2014/0338906, in the name of Monastiriotis et al., discloses polymer-coated proppants for hydraulic fracturing of oil and gas wells have an outer layer portion that comprises an organofunctional coupling agent, preferably an organofunctional silane coupling agent. The use of an organofunctional silane coupling agent in the outer layer portion of the proppant coating is preferably chosen to expose functionalities that will be reactive towards similar functionalities of adjacent and similarly coated proppants so that, when introduced down-hole, these proppants form interparticle bonds at the temperatures and crack closure pressures found down-hole in fractured strata. Such enhanced interparticle bonding helps keep the proppant in the fracture and maintains conductivity with reduced flow-back. The invention also helps proppants designed for low temperature well to bond more firmly and allows proppants designed for high temperature wells to bond well even at lower down-hole temperatures, thereby extending their useful range.
Hudson et al., in U.S. Published Patent Application No. 2015/0034314 describe coated particles, such as proppants, processes for their preparation and methods for using such particles, such as in a hydraulic fracturing process. The coated particles are said to include a coating that includes a crystalline or semicrystalline polyester/polyurethane having a decrystallization temperature of at least 35° C. Hudson et al. make no mention of reducing dust on their proppants.
A need continues to exist in the art for a way to reduce or eliminate dust generated during sand handling for hydraulic fracturing operations.